Finally, we discuss experimental situations.
Assuming that the \(s\) -wave scattering length is 100 Bohr radii and the
bubble radius \(R = 10\)  \(\mu {\rm m}\) , the number of atoms needed is \(N\simeq 1.05 \times 10^6\)  for the condition in Figs. REF  and
REF , and \(N \simeq 1.05 \times 10^5\)  for Fig. REF ,
which is possible in current experimental setups.
Using the mass of a \(^{87}{\rm Rb}\)  atom, we can estimate the rotation
and radial trap frequencies used in Figs. REF  and
REF  as \(\Omega \simeq 2\pi \times 117\)  Hz and \(\omega _t\simeq 2\pi \times 2.3\)  kHz, and the normalized time \(\tau = 0.5\) 
corresponds to 68 ms.
The radius \(R\)  and the radial trap frequency \(\omega _t\)  can be
controlled by choosing the strengths of the DC and AC magnetic fields
producing the bubble-shaped trap [1]}, [2]}.
In experiments, it is difficult to measure the mass-current
distribution.
If nondestructive measurement of vortex positions is possible, the
flow velocity can be obtained from the movement of the vortices.
The real-time imaging technique of vortices may be used for this
purpose [3]}, [4]}.
